This is usually caused because the PostgreSQL database server cannot be accessed, sometimes this is because the service is not running, other times it can be caused by an overzealous firewall or antivirus software. If you previously had PostgreSQL installed for PT3, HEM or HM2 this could also be the cause of the problem. Our support team can help you solve this issue if you file a support ticket, or if you are technically savvy you can solve this issue on your own by following these support guides: https://www.pokertracker.com/guides/PT4/databases